The department's Energy Information Administration said its assessment from reserve additions from 2011 indicated a record in terms of proved oil reserves.
"Crude oil reserves rose 15 percent to the highest level since 1985 and natural gas reserves were up almost 10 percent," the agency said in a report published Thursday.
Texas had the highest level of increase in the EIA report because of ongoing development in shale basins in the state. Production from the Bakken formation in North Dakota pushed the state to the No. 2 spot in terms of oil reserve additions.
The report said natural gas reserve increases in 2011 were the second-highest since 1977. Much of that increase came from Texas and Pennsylvania, which together accounted for 73 percent of the net increase.
Natural gas reserve estimates increased to 348.8 trillion cubic feet in 2011, the 13th annual increase.